The drivetrain of a conventional motor vehicle with an internal combustion engine as the sole drive source normally has a launch element in the power flow between drive source and drive wheels for the purposes of permitting a launch process of the motor vehicle. Examples of such a launch element are hydrodynamic torque converters or friction clutches. The drivetrain of a motor vehicle with an electric motor as the sole drive source generally does not require a launch element because the electric motor can accelerate the vehicle from a standstill.
The drivetrain of a parallel hybrid vehicle normally requires a launch element if it is also sought for a launch process to be performed by the internal combustion engine alone. For the electric launching of a motor vehicle with parallel hybrid drivetrain, numerous variants are known in the prior art. The applicant's patent application publication DE 10 2006 018 058 A1 discloses a variety of launch processes for a motor vehicle with parallel hybrid drivetrain. FIG. 4 shows profiles with respect to time in the case of a purely electrically driven launch process with a slipping converter lock-up clutch, and FIG. 5 illustrates such profiles with a closed converter lock-up clutch. A method for providing the pressure for closing the converter lock-up clutch in the case of launch behavior as per FIG. 5 is not disclosed here.
The patent application publication DE 101 62 973 A1 discloses a hybrid drivetrain of said type, with a mechanical oil pump and an electric oil pump. The mechanical oil pump can be driven by the motor-generator of the drivetrain. The electric oil pump is driven by a dedicated electric motor. The electric oil pump is actuated in a manner dependent on different operating states of the drivetrain in order to supply oil pressure to a hydraulic control device of the transmission.